Communication devices, such as portable radios, are undergoing increasing levels of miniaturization. A typical communication device usually includes an antenna used for receiving and transmitting wireless communication signals. For communication devices operating in the VHF, UHF, and sub-microwave radio frequency ranges, the wavelength of the radio frequency may range between 300 centimeters and 10 centimeters. The communication device requires an antenna of an appropriate length to enable reception or emission of such radio waves. For example, an antenna of simple construction would need to have a conductor having a physical length ranging between 5 and 150 centimeters to accommodate the wavelength of the above-mentioned frequency ranges. For communication devices requiring a compact packaging structure, it might be difficult to accommodate antennas of such lengths. Therefore, it is desirable to have designs which present a physically shorter antenna.
There are many prior art approaches for achieving a shorter physical length antenna. These include the use of helically wound antenna elements, loop antenna elements, and other such designs of varying complexity. Oftentimes, the antenna element is encased for aesthetics, protection, and for other purposes. It is known that if the antenna element is enclosed with a material having a high dielectric constant, the physical length of the antenna required for resonance at certain frequencies is reduced. Such enclosure is known to result in a degradation of performance for the antenna, such as by narrowing the bandwidth, or by reducing the radiation efficiency of the antenna.
It is desirable in the art to have an antenna design with a short physical length suitable for use in miniaturize applications. For some applications, it is also desirable to have a directional antenna. Preferably, this antenna has good performance characteristics and is of simple construction to reduce manufacturing costs.